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Computational fluid dynamics simulation of aerosol transport and deposition

Yingjie TANG, Bing GUO

《环境科学与工程前沿（英文）》 2011年第5卷第3期页码 362-377 doi: 10.1007/s11783-011-0365-8

摘要： In this article computational fluid dynamics (CFD) simulation of aerosol transport and deposition, i.e. the transport and deposition of particles in an aerosol, is reviewed. The review gives a brief account of the basics of aerosol mechanics, followed by a description of the general CFD approach for flow field simulation, turbulence modeling, wall treatments and simulation of particle motion and deposition. Then examples from the literature are presented, including CFD simulation of particle deposition in human respiratory tract and particle deposition in aerosol devices. CFD simulation of particle transport and deposition may provide information that is difficult to obtain through physical experiments, and it may help reduce the number of experiments needed for device design. Due to the difficulty of describing turbulent flow and particle-eddy interaction, turbulent dispersion of particles remains one of the greatest challenges for CFD simulation. However, it is possible to take a balanced approach toward quantitative description of aerosol dispersion using CFD simulation in conjunction with empirical relations.

关键词： computational fluid dynamics (CFD) aerosol transport deposition

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Recent developments in passive interconnected vehicle suspension

Wade A. SMITH, Nong ZHANG,

《机械工程前沿（英文）》 2010年第5卷第1期页码 1-18 doi: 10.1007/s11465-009-0092-z

摘要： This paper presents an overall review on the historical concept development and research advancement of passive hydraulically interconnected suspension (HIS) systems. It starts with an introduction to passive HIS systems and their various incarnations developed over many decades. Next, a description is provided of a recently proposed multidisciplinary approach for the frequency-domain analysis of vehicles fitted with an HIS. The experimental validation and applications of the method to both free and forced vibration analysis are discussed based on a simplified, roll-plane half-car model. A finite-element-method-based approddach for modelling the transient dynamics of an HIS vehicle is also briefly outlined. In addition, recent work on the investigation of NVH associated with HIS-equipped vehicles is mentioned. Discussion is then provided on future work to the further understanding of HIS and its applications. The paper concludes that interconnected suspension schemes can provide much greater flexibility to independently specify modal stiffness and damping parameters – a characteristic unique among passive suspensions. It points out that there is a need for system optimisation, and there are troublesome NVH issues that require solutions. It suggests that further research attention and effort be paid to NVH issues and system level optimisation to gain a greater understanding of HIS and to broaden its applications.

关键词： interconnected suspensions rollover prevention vehicle dynamics ride comfort multibody system dynamics hydraulic system dynamics

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Nonlinear dynamics of a wind turbine tower

A. GESUALDO, A. IANNUZZO, F. PENTA, M. MONACO

《机械工程前沿（英文）》 2019年第14卷第3期页码 342-350 doi: 10.1007/s11465-019-0524-3

摘要： The recent proliferation of wind turbines has revealed problems in their vulnerability under different site conditions, as evidenced by recent collapses of wind towers after severe actions. Analyses of structures subjected to variable actions can be conducted through several methods with different accuracy levels. Nonlinear dynamics is the most reliable among such methods. This study develops a numerical procedure to obtain approximate solutions for rigid-plastic responses of structures subjected to base harmonic pulses. The procedure’s model is applied to a wind turbine tower subjected to inertial forces generated by harmonic ground acceleration, and failure is assumed to depend on the formation of shear hinges. The proposed approach provides an efficient representation of the post-elastic behavior of the structure, has a low computational cost and high effectiveness, and uses a limited number of mechanical parameters.

关键词： nonlinear dynamics plastic shear failure modal approximation time history

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Effect of ligand chain length on hydrophobic charge induction chromatography revealed by molecular dynamics

Lin ZHANG, Yan SUN

《化学科学与工程前沿（英文）》 2013年第7卷第4期页码 456-463 doi: 10.1007/s11705-013-1357-y

摘要： Hydrophobic charge induction chromatography (HCIC) is a mixed-mode chromatography which is advantageous for high adsorption capacity and facile elution. The effect of the ligand chain length on protein behavior in HCIC was studied. A coarse-grain adsorbent pore model established in an earlier work was modified to construct adsorbents with different chain lengths, including one with shorter ligands (CL2) and one with longer ligands (CL4). The adsorption, desorption, and conformational transition of the proteins with CL2 and CL4 were examined using molecular dynamics simulations. The ligand chain length has a significant effect on both the probability and the irreversibility of the adsorption/desorption. Longer ligands reduced the energy barrier of adsorption, leading to stronger and more irreversible adsorption, as well as a little more unfolding of the protein. The simulation results elucidated the effect of the ligand chain length, which is beneficial for the rational design of adsorbents and parameter optimization for high-performance HCIC.

关键词： adsorption desorption irreversibility protein conformational transition molecular dynamics simulation

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Applying system dynamics to strategic decision making in construction

SangHyun LEE

《工程管理前沿（英文）》 2017年第4卷第1期页码 35-40 doi: 10.15302/J-FEM-2017002

摘要： The author discusses the application of System Dynamics to high-level strategic simulation in construction. In particular, System Dynamics’ strength on representing feedback processes, aggregation, soft variables, and continuous simulation clock for high-level simulation are discussed using real modeling examples. From this exercise, it is concluded that System Dynamics offers a great potential for strategic simulation in construction. Further, the author proposes a comprehensive simulation framework that integrates System Dynamics and Discrete Event Simulation for a strategic decision making process in construction where operational details should be taken into account.

关键词： strategic project management construction management system dynamics feedback process hybrid simulation

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Model reduction of contact dynamics simulation using a modified Lyapunov balancing method

Jianxun LIANG, Ou MA, Caishan LIU

《机械工程前沿（英文）》 2011年第6卷第4期页码 383-391 doi: 10.1007/s11465-011-0244-9

摘要：

Finite element models are often used to simulate impact and contact dynamics responses of multibody dynamical systems. However, such a simulation remains very inefficient because very small integration time step must be used when solving the involved differential equations, especially when the involved contact stiffness is high. Although many model reduction techniques have been available to improve the efficiency of finite element based simulations, these techniques cannot be readily applied to contact dynamics simulations due to the high nonlinearity of the contact dynamics models. This paper presents a model reduction approach for finite-element based multibody contact dynamics simulation, based on a modified Lyapunov balanced truncation method. An example is presented to demonstrate that, by applying the model reduction the simulation process is significantly speeded up and the resulting error is bounded within an acceptable level. The performance of the method with respect to some influential factors such as element size, shape and contact stiffness is also investigated.

关键词： contact dynamics dynamic simulation model reduction finite element method

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Nonlinear dynamics and analysis of a four-bar linkage with clearance

Yuanguang TANG, Zongyu CHANG, Xiaogang DONG, Yafei HU, Zhenjiang YU

《机械工程前沿（英文）》 2013年第8卷第2期页码 160-168 doi: 10.1007/s11465-013-0258-6

摘要：

In this paper, nonlinear dynamic behavior of a four-bar linkage considering clearance is studied. The dynamic model of the linkage with a clearance between coupler and rocker is developed firstly. Then the dynamic equations of this mechanism are solved by a numerical method. According to the calculated response, compliance, force and trajectory of pin in joint bearing are obtained. Effects of clearance magnitude and the relationship between a mechanism with clearance and without clearance are studied. By using Poincare Map, it is proved that strange attractors or chaos exist in the dynamic response. In addition, phenomena of chaos, periodic response and subharmonic response also can be found in the special condition. Bifurcation diagram is used to suggest that bifurcation and fractal phenomena exist in the dynamic response of this mechanism.

关键词： four-bar linkage chaos bifurcation strange attractors dynamics

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Water film coated composite liquid metal marble and its fluidic impact dynamics phenomenon

Yujie DING,Jing LIU

《能源前沿（英文）》 2016年第10卷第1期页码 29-36 doi: 10.1007/s11708-015-0388-0

摘要： A composite liquid metal marble made of metal droplet coated with water film was proposed and its impact dynamics phenomenon was disclosed. After encapsulating the liquid metal into water droplets, the fabricated liquid marble successfully avoided being oxygenized by the metal fluid and thus significantly improved its many physical capabilities such as surface tension modification and shape control. The striking behaviors of the composite liquid metal marbles on a substrate at room temperature were experimentally investigated in a high speed imaging way. It was disclosed that such marbles could disintegrate, merge, and even rebound when impacting the substrate, unlike the existing dynamic fluidic behaviors of liquid marble or metal droplet. The mechanisms lying behind these features were preliminarily interpreted. This fundamental finding raised profound multiphase fluid mechanics for understanding the complex liquid composite which was also critical for a variety of practical applications such as liquid metal jet cooling, inkjet printed electronics, 3D printing or metal particle fabrication etc.

关键词： liquid metal marble metallic droplet composite fluid impact dynamics multiphase fluid mechanics

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understanding of interfacial processing mechanism of silicon in water environment: A ReaxFF molecular dynamics

《机械工程前沿（英文）》 2021年第16卷第3期页码 570-579 doi: 10.1007/s11465-021-0642-6

摘要： The interfacial wear between silicon and amorphous silica in water environment is critical in numerous applications. However, the understanding regarding the micro dynamic process is still unclear due to the limitations of apparatus. Herein, reactive force field simulations are utilized to study the interfacial process between silicon and amorphous silica in water environment, exploring the removal and damage mechanism caused by pressure, velocity, and humidity. Moreover, the reasons for high removal rate under high pressure and high velocity are elucidated from an atomic perspective. Simulation results show that the substrate is highly passivated under high humidity, and the passivation layer could alleviate the contact between the abrasive and the substrate, thus reducing the damage and wear. In addition to more Si-O-Si bridge bonds formed between the abrasive and the substrate, new removal pathways such as multibridge bonds and chain removal appear under high pressure, which cause higher removal rate and severer damage. At a higher velocity, the abrasive can induce extended tribochemical reactions and form more interfacial Si-O-Si bridge bonds, hence increasing removal rate. These results reveal the internal cause of the discrepancy in damage and removal rate under different conditions from an atomic level.

关键词： silicon ReaxFF molecular dynamics friction damage

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styrene-butadiene-styrene copolymer on the aging resistance of asphalt: An atomistic understanding from reactive molecular dynamics

《结构与土木工程前沿（英文）》 2021年第15卷第5期页码 1261-1276 doi: 10.1007/s11709-021-0761-5

摘要： To reveal the potential influence of styrene-butadiene-styrene (SBS) polymer modification on the anti-aging performance of asphalt, and its mechanism, we explored the aging characteristics of base asphalt and SBS-modified asphalt by reaction force field (ReaxFF) and classical molecular dynamics simulations. The results illustrate that the SBS asphalt is more susceptible to oxidative aging than the base asphalt under oxygen-deficient conditions due to the presence of unsaturated C=C bonds in the SBS polymer. In the case of sufficient oxygen, the SBS polymer inhibits the oxidation of asphalt by restraining the diffusion of asphalt molecules. Compared with the base asphalt, the SBS asphalt exhibits a higher degree of oxidation at the early stage of pavement service and a lower degree of oxidation in the long run. In addition, SBS polymer degrades into small blocks during aging, thus counteracting the hardening of aged asphalt and partially restoring its low-temperature cracking resistance.

关键词： SBS asphalt oxidative aging asphalt hardening ReaxFF molecular dynamics

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Molecular dynamics study of water diffusion in an amphiphilic block copolymer with large difference in

Yang Zhou, Phillip Choi

《化学科学与工程前沿（英文）》 2017年第11卷第3期页码 440-447 doi: 10.1007/s11705-017-1626-2

摘要： Isothermal-isobaric molecular dynamics simulation was used to study the diffusion mechanism of water in polyurethane- -poly( -isopropyl acrylamide) (PU- -PNIPAm) with a hydrophobic PU/hydrophilic PNIPAm mass ratio of 1.4 to 1 at 298 K and 450 K. Here, the experimental glass transition temperature ( ) of PU is 243 K while that of PNIPAm is 383 K. Different amounts of water up to 15 wt-% were added to PU- -PNIPAm. We were able to reproduce the specific volumes and glass transition temperatures (250 K and 390 K) of PU- -PNIPAm. The computed self-diffusion coefficient of water increased exponentially with increasing water concentration at both temperatures (i.e., following the free volume model of Fujita). It suggested that water diffusion in PU- -PNIPAm depends only on its fractional free volume despite the free volume inhomogeneity. It is noted that at 298 K, PU is rubbery while PNIPAm is glassy. Regardless of temperature, radial distribution functions showed that water formed clusters with sizes in the range of 0.2–0.4 nm in PU- -PNIPAm. At low water concentrations, more clusters were found in the PU domain but at high water concentrations, more in the PNIPAm domain. It is believed that water molecules diffuse as clusters rather than as individual molecules.

关键词： molecular dynamics simulation amphiphilic block copolymer free volume water diffusivity fujita model

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Model reduction techniques for dynamics analysis of ultra-precision linear stage

Xuedong CHEN, Zhixin LI

《机械工程前沿（英文）》 2009年第4卷第1期页码 64-70 doi: 10.1007/s11465-009-0009-x

摘要： Spring-damping elements are used to simplify the internal interaction in the proposed finite element (FE) model of an ultra-precision linear stage. The dynamics behavior is studied. The comparison between mode shapes from the eigenvalue analysis shows that the components, except the translator, can represent system dynamics characteristics. A reduction approach is used to simplify the system in a dynamic studied. There is little difference between the vibration mode and the response analysis. The experimental modal analysis proves the validity of the reduction approach, which can be generalized to the development and dynamics characteristic study of a complex system model to obviously save computational resource.

关键词： dynamics analysis air-bearing linear stage reduction

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Molecular dynamics investigation of mechanical properties of single-layer phagraphene

Ali Hossein Nezhad SHIRAZI

《结构与土木工程前沿（英文）》 2019年第13卷第2期页码 495-503 doi: 10.1007/s11709-018-0492-4

摘要： Phagraphene is a very attractive two-dimensional (2D) full carbon allotrope with very interesting mechanical, electronic, optical, and thermal properties. The objective of this study is to investigate the mechanical properties of this new graphene like 2D material. In this work, mechanical properties of phagraphene have been studied not only in the defect-free form, but also with the critical defect of line cracks, using the classical molecular dynamics simulations. Our study shows that the pristine phagraphene in zigzag direction experience a ductile behavior under uniaxial tensile loading and the nanosheet in this direction are less sensitive to temperature changes as compared to the armchair direction. We studied different crack lengths to explore the influence of defects on the mechanical properties of phagraphene. We also investigated the temperature effect on the mechanical properties of pristine and defective phagraphene. Our classical atomistic simulation results confirm that larger cracks can reduce the strength of the phagraphene. Moreover, it was shown the temperature has a considerable weakening effect on the tensile strength of phagraphene. The results of this study may be useful for the design of nano-devices using the phagraphene.

关键词： phaqraphene mechanical properties crack propaqation molecular dynamics thermal effects

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Mechanical responses of pristine and defective hexagonal boron-nitride nanosheets: A molecular dynamics

Mohammad SALAVATI, Arvin MOJAHEDIN, Ali Hossein Nezhad SHIRAZI

《结构与土木工程前沿（英文）》 2020年第14卷第3期页码 623-631 doi: 10.1007/s11709-020-0616-5

摘要： In this work we conducted classical molecular dynamics (MD) simulation to investigate the mechanical characteristics and failure mechanism of hexagonal boron-nitride (h-BN) nanosheets. Pristine and defective structure of h-BN nanosheets were considered under the uniaxial tensile loadings at various temperatures. The defective structure contains three types of the most common initial defects in engineering materials that are known as cracks, notches (with various length/size), and point vacancy defects (with a wide range of concentration). MD simulation results demonstrate a high load-bearing capacity of extremely defective (amorphized) h-BN nanosheets. Our results also reveal that the tensile strength decline by increasing the defect content and temperature as well. Our MD results provide a comprehensive and useful vision concerning the mechanical properties of h-BN nanosheets with/without defects, which is very critical for the designing of nanodevices exploiting the exceptional physics of h-BN.

关键词： hexagonal boron-nitride mechanical properties crack notch point defects molecular dynamics

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Stability and dynamics of rotor system with 45° slant crack on shaft

Yanli LIN, Xiaohui SI, Fulei CHU

《机械工程前沿（英文）》 2011年第6卷第2期页码 203-213 doi: 10.1007/s11465-011-0131-4

摘要：

Crack on a shaft is one of the common damages in a rotor system. In this paper, transverse vibrations are calculated to compare the influences of transverse crack and slant crack on the rotor system. Results show that the vibration amplitude of the rotor system with a 45° slant crack on the shaft is larger than that with a transverse crack when the two types of crack have the same depth and the rotor system runs in the same condition. Stability and dynamic characteristics of the rotor system with a 45° slant crack on the shaft under torsional excitation are analyzed by considering opening and closing of the crack. It is shown that the instability of the transverse vibration of the rotor system increases with increasing difference between the bending stiffness in two main directions, and the vibration is stable when the two bending stiffness are identical. The spectrum analysis of the steady-state response reveals that the gravity and the eccentricity produce different frequency components, and when the two bending stiffness are identical, the multiple frequency components of the torsional excitation disappear. Further investigation shows that the vibration amplitudes in combined frequencies increase rapidly in transversal, torsional, and axial vibration with increasing slant crack depth. The results are helpful for the understanding the dynamic behavior of a rotor system with a slant crack on a shaft and can be used for the detection of the slant crack on a shaft.

关键词： rotor dynamics slant crack stability torsional excitation open and close